1. Field of the Invention
This invention relates to the preparation of (1) homopolymers and copolymers of a vinyl halide such as vinyl chloride characterized by the properties of small particle size, higher bulk density, reduced plasticizer absorption and easy processability and (2) copolymers of a vinyl halide such as vinyl chloride having improved impact strength properties.
The viscosity of plastisols which utilize extender resins is affected not only by the plasticizer absorption characteristics of the polymers but also by the average particle size, the particle size distribution and the bulk density of the particles. Certain polymers of the invention are particularly useful as extender polymers for this application. These polymers are also useful for the manufacture of films and as coatings for fabrics. The high impact strength polymers of the invention are used in the preparation of moldings.
2. Description of the Prior Art
In an article entitled "Vapor Phase Polymerization of Vinyl Chloride" in the Journal of Applied Polymer Science, Vol. 15, Pages 445-451, 1971, by Kahle et al., a process is disclosed for the polymerization of vinyl chloride utilizing a liquid bulk polymerized polymer as a seed for a subsequent vapor phase polymerization process. The product is said to have reduced plasticizer absorption. In the process, general purpose grade polyvinyl chloride powder is ground to a suitable size to produce small particle size polymer product. Similar processes are disclosed in U.S. Pat. No. 3,595,840 and U.S. Pat. No. 3,622,553.
French Pat. No. 1,588,381 discloses the addition of fresh vinyl chloride and initiator to a vinyl chloride reaction mixture which has already been bulk polymerized to a substantial extent in a single stage reactor and the submission of this mixture to bulk polymerization in order to obtain polyvinyl chloride granules having excellent plasticizer absorption in the cold and in various according to the duration of their dwelling under polymerization conditions.
U.S. Pat. No. 3,583,956 relates to a process for producing vinyl chloride copolymers having a lower softening point than polyvinyl chloride comprising initially polymerizing vinyl chloride to at least 40% conversion, adding a different vinyl monomer in an amount less than remaining unreacted vinyl chloride and continuing the polymerization at a temperature at least 5.degree. centigrade higher than the first polymerization temperature, preferably 10.degree. to 35.degree. centigrade. The specification discloses that the reaction can be carried out in bulk, solution, emulsion or suspension polymerization processes, but only suspension polymerization processes are described in the Examples.
U.S. Pat. No. 3,725,367 relates to the use of a vinyl chloride latex as a seed polymer in a bulk polymerization process to obtain small particle size vinyl chloride particles having a narrow granular size distribution within the range of 10-50 microns.
U.S. Pat. No. 3,687,923 relates to a process for the polymerization of vinyl chloride in bulk comprising polymerizing a portion of the monomer so as to form seeds, and subsequently adding a larger portion of liquid monomer and continuing the polymerization with mild agitation. The amount of monomer used in the first stage of the polymerization should be at least 1/3 by weight of the total quantity of monomer, which is to undergo reaction. An Example shows a product containing 73% particles between 100 and 200 microns in size.
U.S. Pat. No. 3,230,206 relates to a process for the suspension polymerization of copolymers having an heterogeneous structure, good flow properties, and low temperature impact strength by polymerizing acrylic acid esters and vinyl chloride. A portion of the vinyl chloride is added after 5-20 percent of the copolymer is formed.
U.S. Pat. No. 2,961,432 relates to a process for the bulk polymerization of homopolymers and copolymers whereby mixtures of liquid monomers and polymer powders are formed and polymerization carried out. The monomer used corresponds to the same monomer used to form the polymer powder.